Non sedating h1 antihistamines
This adverse effect is linked to their effect on potassium channels leading to slowing of repolarization rate.
H1-antihistamines without sedating effect currently marketed are mequitazine, cetirizine, loratadine, mizolastine, fexofenadine because they do not cross blood-brain and thus their effects remain peripheral.
New H1-antihistamines induce only exceptionally drowsiness. This possibility, even rare, must however be taken into account, particularly at time of a first prescription.
Sedating antihistamines oppose the effects of histamine on H1 receptors in your brain, which is why they cause sedation and drowsiness.
Certain H1 antagonists, such as promethazine, have a local anesthetic effect.
Other H1-antihistamines having an important antimuscarinic activity like diphenhydramine and dimenhydrinate, are used in preventive and curative treatment of motion sickness, but scopolamine which has no antihistamine effect seems more effective than them in preventive treatment.
The drugs of the first antihistamine generation are: promethazine, alimemazine, dexchlorpheniramine, brompheniramine, buclizine, carbinoxamine and doxylamine, are sedating and elicit a drowsiness which can be awkward.
The first-genaration antihistamines have alpha adrenolytic activity which can decrease the vasoconstrictive effect of adrenaline and noradrenaline and an antimuscarinic effect with the corresponding adverse effects.
Azelastine is a H1-antihistamine usable by local route, in nasal pulverization, in the treatment of allergic rhinitis.